It has been a popular practice to wrap a pipe with glass fiber or asbestos to preserve the heat of steam or gas flowing therethrough. Such a practice, however, has the drawback that where the pipe is exposed to water or vibration, the effect of the heat insulation drops or the heat-insulating material is pulverized. For this reason, in some cases, the pipe wrapped with such heat-insulating material is further encircled by another pipe. In such cases, however, with a gap left between the wrapped heat-insulating material and the sheathing pipe, it is unavoidable that the heat-insulating material becomes pulverized when the pipe is exposed to vibration. In order to compensate for these drawbacks, a heat-preserving pipe has been devised which represents a pipe in which the heat-insulating space is filled with foaming synthetic resin, which is later caused to foam, but it lacks heat resistance and is restricted in its applicability.